In fact, when dismantling a nuclear reactor, if it is desired to re-use materials, such as the metals forming part of the installation, it is necessary to establish that the radioactivity percentage of the waste to be removed does not exceed the limit conforming to certain regulations. In this case, this may require a radioactivity of less than 1 Becquerel per gram (1 Bq/g) to achieve this objective, it may also be necessary to observe the ALARA (As Low As Reasonable Achievable) principle which consists of maximum decontamination prior to recovery, as opposed to the fusion of contaminated metals.
Up until now, the control of radioactive contamination is effected with the aid of detectors operational over several square centimeters. The control of contamination on large pieces with the aid of this type of detector requires that these detectors be moved over the entire surface of the piece and a measurement be made after each movement. It is then essential to process the results of each punctual measurement. When dismantling a nuclear reactor where the weight of the material to be removed may exceed four hundred tons, such a conventional method concerning the entire surface of the waste proves to be too random and expensive.